1. Field of the Invention
The present invention relates generally to devices for projecting light beams and more particularly to scatter shields which attenuate off-axis emissions from such devices.
Collimated light beams, particularly collimated laser light beams, are used in a variety of circumstances where it is desired that divergence of a projected beam of light be limited. For example, collimated light beams projected by light beam transmitters may be used for visually aiming firearms, for automatically targeting munitions which can home in on an illuminated spot, or for communicating through free space. When such light transmitters are used in combat situations, the presence of off-axis illumination can act as a beacon revealing the user's position to the enemy. Moreover, when collimated light beams are used for confidential communication, any off-axis illumination may be intercepted by unintended persons in the vicinity, thus compromising the sender's secrecy.
For these reasons, it would be desirable to provide a shielding system for such collimated light beam projectors, which shield system is capable of attenuating off-axis light emissions to a high degree. In particular, it would be desirable if such shield systems could reduce beam scatter to an angle of 10.degree. or less, with scatter beyond this 10.degree. divergence being attenuated by a factor of 100 or more.
2. Description of the Background Art
Light beam transmitters used for visually aiming firearms are generally disclosed in U.S. Pat. Nos. 1,826,004; 3,787,693; 3,867,764; 4,152,754; 4,026,054; and U.S. Pat. No. 4,738,044. A scatter shield for mounting on the front of a light target designator is disclosed in U.S. Pat. No. 4,161,835. The scatter shield comprises a honeycomb structure where the axes of the honeycomb channels are aligned with the direction of the target beam. A mirror-lens assembly for collimating a laser beam is described in U.S. Pat. No. 4,674,011. A lenstube structure for uniformly dispersing a laser light source is disclosed in U.S. Pat. No. 4,744,615. A lens for equalizing a collimated light beam to uniformly illuminate a surface is disclosed in U.S. Pat. No. 4,451,872. U.S. Pat. No. 4,048,489 discloses a light pulse generator which may be mounted on a firearm and triggered when the firearm is discharged. Baffle systems using multiple annular rings for minimizing the reception of stray light by telescopes and other optical equipment are described in MacQueen (1968) Appl. Opt. 7:1149-1154 and Gordon (Abstract WD2D) 1969 Spring Meeting, Optical Society of America. Smith, Modern Optical Engineering: The Design of Optical Systems, McGraw-Hill Book Company, New York, describes a baffle system for an optical receiver employing baffles having converging apertures to trap incoming off-axis radiation and prevent the radiation from reaching the focus of an objective lens.